Marathon bombings come during one of deadliest weeks in U.S.

This photo taken one week after the bombing of the federal building in Oklahoma City shows the damage done by the truck bomb Timothy McVeigh planted. (Source: FEMA)

(RNN) – Monday's bombings at the Boston Marathon happened during a week when Americans were preparing to commemorate some of the most significant tragedies in the nation's history.

The Boston Marathon is annually run on Patriots Day, a state holiday that commemorates the opening battles of the American Revolutionary War in Lexington, MA, and Concord, ME. Although those battles took place on April 19, 1775, the holiday has fallen on the third Monday in April since 1968.

Three of the other tragic events this week either happened on Patriots Day or the anniversary of the battles.

Virginia Tech massacre - April 16, 2007

Tuesday marks the six-year anniversary of the deadliest mass shooting in U.S. history. The shooting on the university's campus in Blacksburg, VA, claimed the lives of 32 people, and 17 others were wounded.

The shooter, Seung-Hui Cho, was a Virginia Tech senior who used two guns in two separate attacks before committing suicide.

Waco siege ends –April 19, 1993

The images of fiery buildings and the ensuing deaths of people inside the Branch Davidian compound in Waco, TX, were seared into people's memory 20 years ago this week.

Followers of David Koresh exchanged gunfire with federal agents during a surprise raid on Feb. 28. Six weeks later, 82 people inside the compound – including children – were killed from either the shootout or as a result of the fire. Four agents also died.

Oklahoma City bombing – April 19, 1995

The bombing at the Alfred P. Murrah Federal Building killed 168 people, including children at a daycare, and became the deadliest domestic terrorist attack in the nation's history.

Army veteran Timothy McVeigh planted a bomb in a truck as retaliation for the way the government handled the Waco raid two years earlier.

Fifteen years later, people still gather annually and read aloud the names of the victims.

Columbine High School - April 20, 1999

Although deadly school violence was not an uncommon occurrence before, the mass shooting in this suburban community brought it into the public consciousness.

Fifteen people died from gunfire - including students Eric Harris and Dylan Klebold, who committed suicide - and 21 more were inured.

Police teams also found numerous explosive devices throughout the school. The journals of the teenage shooters revealed that they intended to commit a crime more infamous than the Oklahoma City bombing.